Question

The relative rate of radical bromination is 1:82:1640 for 1 degree:2 degree:3 degree hydrogens, respectively. Draw all of the monobrominated products that you might obtain from the radical bromination of the compounds below. Calculate the relative percentage of each. a methylcyclobutane b. 3,3-dimethylpentane c. 3-methylpentane

Answer 1

The selectivity of the radical reactions can be predicted mathematically based on a combination of an experimentally determined reactivity factor, R_i, and a statistical factor, nH_i. In order to use the equation shown below we need to look at our original alkane and look at each H in turn to see what product it would give if it were to be susbtituted.

1.

a. we have three types of H, the 3 x 1^o in -CH₃ and the 6 x 2^o , 1 × 3^o .

%1 = 100 x (3 x 1) / (3 x 1 + 6 x 82 + 1*1640) = 300/2135 = 0.14%

%2 = 100 x (1 x 1640) / (3 x 1 + 6 x 82 + 1*1640) = 76.8%

%3 = 100 x (4*82) / (3 x 1 + 6 x 82 + 1*1640) = 15.36%

%4 = 100 x (2*82) / (3 x 1 + 6 x 82 + 1*1640) = 7.7%

Apply same method for the other two molecules.